Preparation of O-(2-hydroxyalkyl)oximes

ABSTRACT

Preparation of O-(2-hydroxyalkyl)oximes I ##STR1## (R 1  and R 2  =alkyl or R 1  and R 2  and the C atom which carries them=5- to 7-membered cycloalkyl), by catalytically hydrogenating an O-(2,3-epoxyalkyl)oxime of the general formula II ##STR2## using hydrogen. The products I are suitable as intermediates for herbicides.

This application is a 371 of PCT/EP95/02932 Jul. 25, 1995.

The present invention relates to a process for preparingO-(2-hydroxyalkyl)oximes of the general formula I ##STR3## where R¹ andR² are each alkyl groups having 1 to 10 carbon atoms or, together withthe carbon atom which carries them, are bonded to give a 5- to7-membered cycloalkyl radical.

O-(2-Hydroxyalkyl)oximes are of great importance as intermediates forcrop protection agents (cf. eg. the earlier German Application DE-A 4415 887).

In the preparation of compounds of the type I by O-alkylation ofhydroxylamines, to a certain extent the compound isomeric to I whichcarries the CH₃ group on the C atom which is adjacent to the oximeoxygen is also always formed.

The previously described hydrogenations of oxiranes lead either to theprimary alcohol or to a mixture of secondary and primary alcohol (cf.eg. U.S. Pat. No. 4,064,186 and Houben-Weyl, Methoden der OrganischenChemie Methods of Organic Chemistry!, Georg Thieme Verlag, Stuttgart,Vol. 6/3, 4th Edition, 1965, pages 442-446).

It is an object of the present invention to provide a process whichleads with higher regioselectivity and substantially without formationof by-products to the O-(2-hydroxyalkyl)oximes I.

We have found that this object is achieved by a process for preparingthe O-(2-hydroxyalkyl)oximes of the formula I, which comprisescatalytically hydrogenating an O-(2,3--epoxyalkyl)oxime of the generalformula II ##STR4## using hydrogen.

In the following, the Houben-Weyl literature references relate to:Houben-Weyl, Methoden der Organischen Chemie (Methods of OrganicChemistry), 4th Edition, Thieme Verlag, Stuttgart.

Among the compounds I which can be prepared by the process according tothe invention, those are preferred in which R¹ and R² each are a C₁ -C₄-alkyl group and especially a C₁ -C₃ -alkyl group, or, together with thecarbon atom which carries them, form a cyclopentyl or cyclohexyl ring.Particularly preferably, R¹ and R² are each methyl or ethyl, inparticular both methyl.

The O-(2,3-epoxyalkyl)oximes II are generally known or are obtainable byknown methods, especially by base-catalyzed reaction of thecorresponding epihalohydrins with the free oximes in a dipolar aproticsolvent (cf. eg. Zh. Org. Khim. 5 (1969), page 1353 to page 1355).

Suitable catalysts for the hydrogenation are catalysts generallycustomary for this purpose, as are described e.g. in Houben-Weyl, Volume4/1c.

Preferred hydrogenation catalysts are those which comprise a metal fromgroups 8 to 10 according to the IUPAC classification of the PeriodicTable, preferably from the group consisting of the elements cobalt,ruthenium and rhodium, especially from the group consisting of theelements platinum and nickel, and in particular palladium.

The catalysts can be used as such or preferably on a support. Customarysupport materials such as silica, alumina, titanium dioxide, silicatesand zeolites and especially activated carbon are suitable.

For preparation of the supported catalysts binders or shaping aids canbe additionally used. The catalysts can be employed in the form ofchips, extrudates, tablets or balls.

In general, 0.1 to 2, preferably 0.1 to 1%, by weight of catalyst areemployed per mole of the compound II to be hydrogenated, thesequantitative data relating to the active mass of the catalyst withoutsupport materials.

The hydrogenation can be carried out continuously or, preferably,batchwise.

In batchwise procedure in the liquid phase, the hydrogenation can becarried out in the presence of a solvent. Suitable solvents are polarsolvents such as ethers and alcohols as well as mixtures thereof.Preferred solvents are ethers or alcohols having up to 6 carbon atomssuch as 1,2-dimethoxyethane, ethanol, n-propanol, isopropanol andn-butanol.

The pressure can be selected within wide limits which extend from 1 to400 bar, but the reaction is preferably carried out in a pressure rangefrom 1 to 100, especially from 10 to 70 and in particular from 30 to 50bar.

The temperature during the hydrogenation is preferably 0 to 100,especially 10 to 50 and in particular 25° to 30° C.

The reaction products I are isolated by methods known per se, preferablyby distillation. The yield of the compounds I is normally from 70 to90%, with a selectivity of, as a rule, over 98%.

The O-(2-hydroxyalkyl)oximes I obtainable by the process according tothe invention are suitable as precursors for herbicides, in particularof the cyclohexenone type (cf. eg. DE-A 44 15 887).

EXAMPLE Preparation of 2-propanone O-(2-hydroxypropyl)oxime

130 g (0.94 mol) of 2-propanone O-(2-epoxypropyl)oxime (cf. EP-A 23 560;Zh. Org. Khim. 5 (1969), pages 1353 to 1355) and 600 ml of ethanol weretreated with 4 g of palladium/carbon (10% by weight palladium) and themixture was hydrogenated at 25° C. and a hydrogen pressure of 50 bar.After 17 hours the reaction was complete. The catalyst was filtered off.The solvent was then removed and the residue was distilled through apacked column of length 50 cm and diameter 5 cm, which was packed withwire mesh rings of diameter 3 mm (b.p.: 74° C./20 mbar).

The yield of 2-propanone O-(2-hydroxypropyl)oxime was 84%, with a purityof 99.8%. Isomeric 2-propanone O-(2-hydroxy-1-methyl-ethyl)oxime was notformed in this case.

We claim:
 1. A process for preparing O-(2-hydroxyalkyl)oximes of thegeneral formula I ##STR5## where R¹ and R² are each alkyl groups having1 to 10 carbon atoms or, together with the carbon atom which carriesthem, are bonded to give a 5- to 7-membered cycloalkyl radical, whichcomprises catalytically hydrogenating an O-(2,3-epoxyalkyl)oxime of thegeneral formula II ##STR6## using hydrogen.
 2. A process as claimed inclaim 1, wherein the starting material used is anO-(2,3-epoxyalkyl)oxime where R¹ and R² are methyl.
 3. A process asclaimed in claim 1, wherein the catalyst used is an element of groups 8to 10 of the Periodic Table.
 4. A process as claimed in claim 1, whereinthe catalyst used is palladium, if desired on a support.